EMG electrode

ABSTRACT

An electrode for collecting surface electromyographic (EMG) signals consists of a generally bolt-shaped structure having a circular signal-gathering head and an integral shaft for support purposes and for transmission of electrical signals. The head of the electrode is configured as a disc having a plurality of pyramids distributed substantially evenly over the signal gathering surface with the tips of the pyramids projecting outwardly of the head for contact with the skin of a patient. Preferably, the electrode consists entirely of 316L stainless steel, the pyramids are formed by grinding or electromachining and the shaft is threaded for receipt of a clamp nut. The electrode is adapted for mounting in a hole in a thin, flexible support member by means of the shaft to maintain spacing among adjacent electrodes and to assure proper contact with the patient.

This application claims benefit of provisional application 60/043,092Apr. 15, 1997.

TECHNICAL FIELD

This invention relates to a method and apparatus for monitoring anddisplaying the condition of muscles in a muscle group by the sensing andanalysis of electromyographic signals derived from a non-invasive bodysurface electrode array positioned close to the muscle group.

BACKGROUND ART

Knowledge of the presence of electromyographic (EMG) signals in themuscles of humans, and the change of these signals with muscle activity,spawned development of electronic devices and techniques for monitoringthose signals for the evaluation of the muscles. Human musculature,however, involves many hundreds of muscles in various muscle groups,which interact to provide skeletal support and movement. Much of therecent development has been concerned with the techniques and/or devicesfor monitoring the signals, analyzing the information obtained andproviding reliable and useful data for the patient or treatingphysician. Recent developments in computer technology have also providedan assist in this regard. With higher speeds of operation and greatercomputing capacity, the capability for handling and operating upon amultiplicity of signals in a reasonable evaluation period has becomefeasible. However, because of the complexity of the muscle structure andthe difficulty in obtaining useful, reliable signals, preferably in anon-invasive mode, obtaining a useful definition of the muscle activityin a reasonable amount of time and in an economical manner is stillsubject to current development.

Typical of this prior art is the device described by D. Prutchi in thepublication "A High-Resolution Large Array (HRLA) EMG System", publishedSeptember 1995 in Med. Eng. Phys., Vol. 17, 442-454. Prutchi describes abracelet which may be wrapped about a body limb and which contains 256surface electrodes to record the electrical activity of underlyingmuscles. The electrodes are arranged in eight groups of thirty-twoelectrode linear arrays directly connected to buffer boards in closeproximity of the electrodes. Further processing of the electricalsignals is performed to provide a desired signal analysis, in thisinstance primarily being concerned with the bidirectional propagation ofa compound potential in a single muscle in the upper arm of a humansubject or a histogram of total power contribution from active fibers ina subject muscle, both being presented in charted format.

U.S. Pat. No. 5,086,779 to DeLuca, et al., describes a back analysissystem of plural electrodes coupled to a computer system for processingthe signals and to provide graphical representations of results.DeLuca's invention relates primarily to isolating particular musclegroups by the use of support and restraint devices which limit themovement of the patient's torso in predetermined patterns correlated tothe desired muscle groups. DeLuca's electrode array consists of separateelectrodes individually placed at desired locations on a patient's back.

U.S. Pat. No. 5,058,602 to Brody describes a method of electromyographicscanning of paravertebral muscles comprising measuring electricalpotentials bilaterally across segments of the spine. Readings arecategorized into different patterns which are indicative of differentmuscular conditions. Brody suggests equipment useful within hisdescribed techniques as an available EMG scanner having electrodesspaced 2.5 cm apart and a computer component, but provides few detailson the equipment or an indication of usefulness for isolating certainmuscles or muscle groups.

U.S. Pat. No. 5,318,039 to Kadefors, et al., describes a method andapparatus for detecting electromyographic signals, processing them andproviding an indication of the change of the signal from a predeterminednorm. Kadefors' electrode system comprises three electrodes, one ofwhich is a reference marker. This electronic apparatus, in essence,includes a sample and hold function in which current responses can becompared to earlier responses and an indication provided based on thedifferences detected.

U.S. Pat. No. 5,505,208 to Toormin, et al., describes a method fordetermining the status of back muscles wherein EMG signals are monitoredfrom a number of electrodes placed in a pattern on a patient's back, theactivity of each electrode is determined and the results stored. Adatabase of results provides a standard from which comparisons can bemade to determine deviations or abnormalities, as a device for the careand management of the patient's dysfunction.

U.S. Pat. No. 5,513,651 to Cusimano, et al., describes a portableelectronic instrument for monitoring muscle activity, using standard ECGelectrodes and a computer for analyzing the detected signals. Theelectrodes are applied individually at predetermined locations and arange of motion device is employed to generate signals related to aparticular muscle group. Output plots are produced to provide anindication of results, apparently in the form of printouts ofinformation reflecting any deviations from the norm of expected muscleactivity.

While the prior art devices describe much sophistication in thedetection and analysis of EMG signals, there is a need for equipmentwhich is capable of being utilized by the average skilled examiningphysician who, for example, uses and is familiar with the techniques ofphysical examination and palpation of the paraspinous musculature of thethoracolumbosacral spine.

DISCLOSURE OF INVENTION

An object of the present invention is to provide improved surface EMGequipment, readily useable by the skilled examining physician, for thediagnosis or treatment monitoring of patients with low back pain.

A further object of the present invention is to provide an improvedclinical tool which is portable and which uses non-invasive techniquesfor the collection of signals.

A further object of the present invention is to provide improved EMGequipment which provides a visual display of the activity of muscles ormuscle groups.

A further object of the present invention is to provide improved EMGequipment in which the visual display of muscle activity is juxtaposedover a visual display of normal muscle anatomy for correlation by theexamining physician.

A further object of the present invention is to provide improved EMGequipment in which the visual display can be selected for specificmusculature identified by the examining physician.

A further object of the present invention is to provide improved EMGequipment which utilizes a single detector pad of electrodes in whichthe electrodes are arranged in a specific array, to monitorinstantaneously all specific muscles in a muscle group of a patient.

Further objects of the present invention will be made apparent in thefollowing Best Modes for Carrying Out the Invention and the appendedClaims.

The electromyographic (EMG) diagnostic system of the present inventionis particularly suited for evaluation of the lower back of a human andconsists essentially of a sensor pad for collecting and conditioning EMGsignals, electronic equipment including a computer for signaldiscrimination and evaluation and a display device for providing avisual display of the activity of selected musculature. A groundelectrode is positioned on the patient. The electronic equipment servesto receive signals from the sensor pad which is pressed against thelower back of a patient in a predetermined location and held immobilerelative to the patient such as by strap with foam backing, aninflatable bladder, an adhesive pad or other convenient arrangement.Signals from individual electrodes are conditioned by the electricalequipment, discriminated from noise signals and the like and evaluatedrelative to the signal received from the reference electrode. Computerapparatus is then used to analyze the signals, and can combine thesignals in various patterns to provide an analysis of the muscularanatomy of the lower back and the activity of such muscles.

A preferred technique for signal monitoring is to determine the RMSvoltage of the sensed signals over a predetermined time interval. TheRMS voltage is converted to a visual display representative of the powerlevel, which display then provides a visual indication of thoselocations where a higher level of muscle activity is detected. The RMSsignal technique is advantageous in providing a device for averaging thehighly sensitive and often variable individual electrode signals whichare susceptible to changes in contact resistance at the electrode, thehuman skin resistance, stray field fluctuation, inadvertent movements bythe patient, and the like, which can introduce false signals, and maskthe desired muscle activity signals.

A visual display of the sensed muscle activity is provided on a monitor,such as a cathode ray tube type monitor, which may then be evaluated bythe attending physician. A predetermined display of normal back anatomyis displayed simultaneously on the monitor to assist the physician inhis evaluation. For example colorization of the resultant sensed displaywith different colors representing the degree of contraction thusprovides a vivid indication of abnormal activity of the muscle. Normalback anatomy is provided in this invention by the selection from aninventory of various back muscle configurations which depict differentlayers of back muscles of the normal human patient. These configurationsare selectable by the physician for comparison with the sensed muscleactivity pattern in order to assist in providing a correlation betweenthe two. Further control is provided in that the physician not only canalter the physical configuration of the sensed signal display but alsocan adjust the intensity or colorization of the sensed display to rendera more pronounced image of abnormal muscle activity relative to normalback anatomy. Visual display modification is achieved by adjustment ofthe sensitivity of the sensed signal detector or by increasing the levelof signal over which a visual indication is provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a simplified schematic overview of a portion of the lower backskeletal structure of a patient with an outline of the sensor padportion of the invention depicted in position thereover.

FIG. 2 is a schematic view of the apparatus of the invention, comprisingthe sensor pad in connection with electronic apparatus including acomputer and display unit.

FIG. 3 is a schematic view of the screen of the display unit of theinvention showing a full color bar matrix overlay in relation to thelower back skeletal anatomy of a human patient.

FIG. 4 is a view partly in cross-section of a portion of the sensor padof the invention, showing a single electrode and the electricalconnection to the computer portion of the invention.

FIG. 5 is an enlarged plan view only of the single electrode shown inFIG. 4.

FIG. 6 is a cross-sectional view of a single electrode taken along thelines 6--6 of FIG. 5.

FIG. 7 is a schematic view of the screen of the display unit of theinvention depicting the location of a portion of the electrodes of thesensor pad as circles and showing several interconnecting color bars.

FIG. 8 is a schematic view of the lower torso of a patient with thesensor pad held in position by a retaining belt and a support pad.

FIG. 9 is a plan view with parts removed of the retaining belt of FIG.8, showing the support pad.

FIGS. 10-13 are schematic views of the screen of the display unitshowing various configurations of color bar displays.

FIG. 14 is a schematic diagram of skeletal anatomy associated with thelower back of a normal human patient.

FIGS. 15-23 are schematic diagrams of various groups of musculature of anormal human patient shown in relation to the skeletal anatomy of FIG.14.

FIG. 24 is a schematic view of the apparatus of the invention, similarto that of FIGS. 2 and 4, in a modified showing of the interrelation ofcomponents of the invention.

FIG. 25 is a schematic view of the components comprising the AnalogSignal Conditioning Subsystem of FIG. 24.

FIG. 26 is a schematic view of the components comprising the SignalProcessing Subsystem of FIG. 24.

FIG. 27 is a logic diagram showing the data flow in the software of thesystem.

FIG. 28 is a chart of a portion of the software program of theinvention, showing a header format.

FIG. 29 is a chart of a portion of the software program of theinvention, showing a listing of files developed therein.

FIG. 30 is a chart of a portion of the software program of theinvention, showing generally the Source File Structure.

BEST MODES FOR CARRYING OUT INVENTION

Referring now to the drawings, and initially to FIG. 1, there is shownin schematic form the sensor pad 10 of the invention positioned inrelation to a partial skeletal showing of the lower back of a patient,the latter comprising a spine 11, left posterior superior iliac crest12, right posterior superior iliac crest 14, portions of the scapula 15and ribs 16. As will be described in greater detail hereafter, sensorpad 10 is a device for collecting electromyographic (EMG) signals fromthe underlying muscle structure supporting and providing movement to thespine 11. The muscle structure is a complicated array of musclesconsisting of at least sixty-nine erector and intrinsic muscles in thethoracolumbosacral spine extending from about the tenth thoracicvertebrae 18 to the sacrum 20. These are the primary muscles with whichthis invention is concerned and occur in layers from deep tosuperficial. Also formed in the superficial region of the lower back areseveral muscles which are not classical erector muscles, which whileimportant, are not the principal interest of this invention. Theselatter muscles may also produce EMG signals which serve to complicatethe evaluation process and may require discrimination, but which are nota primary source of the lower back pain syndrome affecting the greaterportion of the patient population.

EMG signals and their relation to muscle functions are well understoodat the current state of investigations. Muscles are controlled bynerves, the latter transmitting an electrical signal to a particularmuscle and causing contraction thereof. The muscle itself is a volumeconductor reacting to the signal of the associated nerve. There is avoltage change that occurs when a muscle contracts creating an electricpotential that is directly proportional to the strength of contractionand that can be captured from the external surface area of the patient,in this instance being the surface area of the thoracolumbosacral spine.Currently, there is technology which allows certain evaluations of theelectrical activity of muscles such as EMGs or EKGs and which may bedisplayed in analog, waveform or spectral forms. Available technologyand the associated devices however are deficient in not being able toselect all muscles in a muscle region in a manner which is conducive toevaluation by an attending physician.

Referring now to FIG. 2 there is shown in schematic form, the essentialelements of this invention as comprising sensor pad 10 and electronicapparatus 22 comprising preamplifier 23, converter 24, computer 25 anddisplay unit 26. Sensor pad 10 is a flat rectangular piece ofsiliconized rubber, approximately 0.062 inch thick, measuring about12×12 inches and with a Durometer hardness on the order of 20 to 40. Onesource for sensor pad 10 is Fairprene Industrial Products, Inc. ofFairfield, Conn.

Sensor pad 10 further comprises an array of sixty-three electrodes 28,preferably made of 316L stainless steel. Electrodes 28 are arranged in a7×9 pattern, with the electrodes in each row and column being spaced1.162 inches apart on center. A central column 29 of nine electrodes 28is located in the middle of sensor pad 10 to overlay the spine 11 of thepatient, and three equally spaced parallel columns of nine electrodeseach are positioned on either side of the central column 29. Similarly,a central row 30 of seven electrodes 28 is positioned near the center ofsensor pad 10, and four parallel rows of seven electrodes each arepositioned on either side of central row 30. Ground electrode 31, is astandard electrode preferably positioned on a wrist of the patient.

All of the electrodes 28, are identical and one configuration is shownin greater detail in FIGS. 4-6 as comprising a pyramidal tipped,bolt-shaped structure having a head 32 and integral threaded shaft 34.Head 32 is circular and includes a plurality of pyramids 35 distributedsubstantially evenly and projecting outwardly of the upper surface ofhead 32 to form the patient-contacting surface of electrode 28. Head 32is preferably 0.375 inches in diameter and has a thickness of 0.08inches from the lower surface thereof at the junction with shaft 34, tothe tips 36 of pyramids 35. Pyramids 35 are formed by grinding electrodehead 32 in a series of parallel and orthogonal passes or byelectromachining to produce a square pyramidal shape having an altitudeof 0.042 inches, an angle of 90 degrees between opposing pyramid facesand culminating in a tip 36 having a radius of 0.005 inch. Tips 36 arespaced 0.094 inches from one another and in this embodiment of theinvention, result in an electrode 28 having twelve pyramids 35 and tips36 at the signal-collecting surface thereof. It has been determined thatthis configuration of electrode 28 is particularly useful in enhancinglower contact resistance when placed in position on a patient, therebyassuring better EMG signal reception and greater accuracy of themeasurement.

Each electrode 28 is mounted in an aperture in sensor pad 10 andretained in position by a nut 170 threaded to shaft 34. Alternatively,electrode 28 may have an unthreaded shaft 34 and be retained in positionby a push connector. A solderless ring connector 38 is also received onshaft 34 and is firmly secured by outer nut 39 to provide an electricalinterconnection with the signal gathering surface of electrode 28. Anelectrode wire 40 is crimped to connector 38 and each of the electrodewires 40 is routed over the surface of sensor pad 10 to a pigtail at theupper end of sensor pad 10 which terminates at a connector 41. Eachelectrode wire 40 is preferably a 30 gauge, multi strand, flexiblecopper wire which allows for some deformation of sensor pad 10 toconform to the lower back of a patient, while connector 41 allows forreleasable connection of the sensor pad to the electrical circuitry tofacilitate substitution of components of the apparatus of the invention.With an electrode head 32 diameter and spacing, as mentioned in thepreferred embodiment, the edge to edge spacing of electrodes 28 in eachcolumn 29 and row 30 is 2.0 centimeters or approximately 0.79 inches.This has been determined to provide enough distance between electrodes28 to result in a meaningful signal difference between electrodes.

The electronic circuitry comprising preamplifier 23 is located nearsensor pad 10 for conditioning and amplifying the signals received atelectrodes 28. Electrode wire 40 is connected to buffer amplifier 42,and the signal in turn is routed to low pass filter 43 and high passfilter 44 for each electrode 28 of sensor pad 10. Conditioning of thesignals preferably occurs closely adjacent the patient and avoids remotetransmission of very low level signals in a background of randomlygenerated noise signals. Buffer amplifier 42 minimizes leakage currentthrough the electrode and errors due to electrode impedance changes.High pass filter 44 serves as an anti-aliasing filter, and low passfilter 43 prevents saturation of analog to digital (A/D) converter 24 byoffset voltages, such filters being well understood in the art.

As shown in FIG. 24 preamplifier 23 includes Buffer/Amplifier module 42and Filter/Buffer module 105. Cable 45 connects the components ofpreamplifier 23 to analog to digital (A/D) converter 24 for transmissionof the electrode signals for further processing and analysis.

Sensor pad 10 is applied to the back of a patient by orienting certainof the electrodes 28 to the skeletal structure of the patient. Thecentral electrode in the top row of electrode rows 30, i.e., electrode46 is located over the spinous process of the tenth thoracic vertebrae18. Two other landmarks are identified in a similar manner as the sensorpad 10 overlays the mid portion of the posterior superior iliac crest(PSIS). For example, the second and fifth electrodes 33,37 respectively,in the center row of electrode rows 30 may be over the left PSIS andright PSIS. Alternatively, other landmarks may be used, such as anelectrode overlying the fourth lumbar vertebrae, or other physiologicalreference point. This calibration information is then fed into theelectronic apparatus 22 for appropriate adjustment of the voltage datareceived from electrodes 28 and subsequent visual display relative topredetermined displays of muscular anatomy appearing at display unit 26,in order to assure standardization of electrode placement.

Referring now as well to FIGS. 8 and 9, there is shown in two views themechanism for attachment of sensor pad 10 to the lower back of a humanpatient 48. A type of lumbar support belt 49 encircles part of the lowertorso of patient 48 and is retained in place by several straps 50 ofnon-elastic web culminating in quick release snaps 51 at the endsthereof for adjustment and securement. Belt 49 includes a pouch thereinin which is disposed a molded foam pad 52. Pad 52 is generallyrectangular in configuration and about one inch in thickness at itsmidpoint and tapering to about 1/8" thickness at its left and rightedges. The pad has a curved inner surface generally conforming to thecurvature of the lower torso of a typical patient 48 and overlyingsensor pad 10 to press the latter into secure physical contact withpatient 48 as straps 50 are adjusted. Preferably, belt 49 is about twoinches larger than the operative portion of sensor pad 10, and pad 52 isalso slightly larger than sensor pad 10, thereby to overlap the latterand assure fairly uniform pressure over the entire area of sensor pad 10and consistent readings from electrodes 28.

Preferably, pad 52 has three parts, namely parallel vertical sections 53and a central stiffer section 54. Pad 52 is firm, yet flexible, andthicker in the central section 54 than in the outer sections 53 asdescribed above. In this manner a better fit is made to accommodate thecontour of the human back. Support belt 49 is preferably made ofnon-elastic nylon material as are straps 50 to achieve a secure andreliable connection to the patient 48.

Preferably, a conductive gel is applied to electrodes 28 to enhanceconductivity of the interface between electrodes and patient 48, as iswell known in the art. One suitable brand of water soluble gel is thatmanufactured by TECA, a subsidiary of Vickers Medical, Inc.

Once sensor pad 10 has been located in position on a patient 48 andsecured by support belt 49 and electrical interconnection made withelectronic apparatus 22, the patient can be moved about and put througha series of different positions in order to develop a series of signalgroups indicative of the underlying musculature. Typically, thesepositions are neutral, flexion, extension, left flexion, right flexion,left rotation, right rotation, sit, supine and prone, although variousmodifiers may be added to these positions. In each of the positions ascan of the electrodes 28 is made, each scan requiring only 1-10seconds, and the signal information retained for later utilization inelectronic apparatus 22.

Electrical signals from electrodes 28 are connected by way of wires 40,buffer amplifier 42, filters 43, 44 and cable 45 to analog to digital(A/D) converter 24 and then to computer 25 for analysis and conversion.A/D converter 24 is a standard converter device, one suitable versionbeing board no. AT-MIO-64-E3, manufactured by National InstrumentsCompany. The data from sensor pad 10 is collected in pseudo differentialfashion, each electrode 28 being sampled relative to reference electrode61 located in the center of pad 10. Subtraction of electrical datayields the wave form between the two electrodes of interest and the waveform is subjected to a root mean square (RMS) analysis over apredetermined time interval to yield a discrete number indicative of thesignal strength. In one example of utilization of the signals, the RMSnumber is converted to a representative color indicia and that colorindicia is displayed on the screen of display unit 26 in a locationrepresentative of the particular two electrodes 28 of interest.

This technique of measurement may best be seen in the FIG. 7representation of a portion of the screen 62 of display unit 26. Herethe electrode positions are represented by circles with alphanumericdesignations therein, with the seven columns of electrodes 28 designatedfrom A-G and the nine rows designated from 1-9. Thus, various electrodepositions are shown, for example, as C4, D5, E6 with D5 representativeof the reference electrode 61 position. Intermediate computer generatedlight bars or line segments 63 interconnect various ones of the adjacentelectrode positions, i.e., C5-D5 and C6-D5 to represent the pattern ofimage generated by computer 25 and displayed at screen 62 of displayunit 26.

A full pattern display is shown in FIG. 3 wherein the screen 62 ofdisplay unit 26 shows the full array of light bars 63 interconnectingall of the electrode 28 positions, in a matrix overlying a display ofthe lower back skeletal anatomy 90 of the patient 48. This viewdemonstrates the spatial relationship among the locations of electrodes28, the visual display of light bars 63 and the patient 48 anatomy 90 ina manner that can be readily visualized and utilized by the examiningphysician. It will be described in greater detail hereinafter that thelight bar 63 display can be adjusted or modified by the physician, orautomatically by the computer to produce effects including a morelimited visual display of light bars 63, or variations in intensity, hueor colorization thereof to enhance the desired display. Further, it willbe shown that instead of the skeletal structure 90 of the patient 48,various depictions of the standard musculature of the patient such asthose templates shown in FIGS. 15-23 can be made to induce a correlationbetween the signals being obtained from the sensing electrodes and thespecific musculature creating the abnormal condition affecting thepatient.

In a scan of the complete array of electrodes 28, 206 color bar imagesare produced on display unit 26 in positions delimited by andcorresponding to the positions of the electrodes 28 on sensor pad 10.Also superimposed on display unit 26 is a graphical depiction of themusculature of the lower back of patient 48 with correlation between thetwo being achieved by the registration process previously describedwhere a sensor pad is located relative to the tenth thoracic vertebrae18 and the PSIS identifying crests 12, 14.

In a preferred embodiment of the invention the diagrams of themusculature of FIGS. 15-23, may be shown at the screen of display unit26 as a series of images, each representative of certain muscle groupsof the lower back of patient 48 so that the attending physician mightmake a correlation between the colors which represent the strength ofcontraction of the muscle underneath the electrode and the particularmuscles or muscle groups, and discern what muscle is causing theparticular colorization patterns being produced. It is apparent as well,that it would be possible to program computer 25 to recognize abnormalsignals from the electrodes 28 being polled to provide some otherindication of the abnormal situation using different evaluationtechniques. It is also apparent that the signals collected fromelectrodes 28 can be stored in a database and processed in differentways, perhaps at later times or printed out in hard copy, if this is adesired result. The capture of data from all of the electrodes 28 occurssubstantially simultaneously and is stored in computer 25 formanipulation in a myriad of possible ways, only certain of which aredescribed herein.

Referring now to FIGS. 10-13, there are shown several variations of thetechniques for monitoring and analysis of the electrical signals derivedfrom electrode 28. As previously described, each electrode 28 is scannedrelative to reference electrode 61 to develop a signal representative ofthe voltage level detected at the site of the particular electrode, anddata representative of the signal retained in computer 25. In furtherprocessing of the signals, each signal may be compared to that of otherelectrodes to develop signal patterns representative of the musclecondition being evaluated. For example, FIG. 10 is a representation ofsignals developed at sensor pad 10 when only a depiction of a discretecolor dot is made at the location of each electrode 28, with no showingof color bars. This display might be most useful in achieving a desiredregistration between electrode 28 display and the skeletal structure 90display.

FIG. 11 describes a first variation for analysis of the signals wherethe signal of each electrode 28 in the first row 64 is compared to thecorresponding electrode 28 in the same column, in the second row 65 todevelop a resultant signal, represented at display unit 26 as a bar 66joining the location of the particular electrodes. In this manner a fullpattern of vertical bars 66 is developed, although only a portion isshown, with each being a unique color and representative of the signalcomparison at each electrode pair. Such arrangement of color bars 66 maybe displayed juxtaposed to patterns of muscle structure as previouslydescribed, and likely is more useful in displaying an association withmuscles or muscle groups which are oriented generally vertically in theback of the patient.

FIGS. 12 and 13 represent yet other variations of signal analysiswherein different herringbone patterns of signal are derived. In FIG.12, for example, the signal of center electrode 70 in the second row,center column (D2) is compared with electrodes 71, 72 in the first rowand adjacent columns (C1) (E1) to develop intermediate color bars 74, 75respectively, indicative of the comparison of the electrode signals.Further color bars corresponding to bars 74, 75 are developed throughoutthe array of electrodes 28 to achieve an overall pattern for display atdisplay unit 26. Again, only a portion of the display is depicted inFIG. 12, for purposes of clarity.

FIG. 13 is yet another variation of a display that may be produced usingthis technique of monitoring. Here an inverted herringbone patternconsisting of color bars 78 is achieved when the signals from electrodes28 are compared in the described pattern. For example, electrode 79 inthe first row, center column (D1) is compared to electrodes 80, 81 inthe second row in adjacent columns (C2) (E2) to produce the intermediatecolor bars 78. When extended throughout the array of sensor pad 10, acolored herringbone pattern of color bars 78 is achieved for comparisonwith muscle pattern displays shown in association therewith.

It is apparent that still further comparisons can be made of the signalsobtained from electrodes 28, for example to compare the signal of eachelectrode 28 with the signals of all adjacent electrodes 28, andelectronically summarize the information obtained and to produce arepresentative color pattern of the results for visualization at theface of display unit 26.

Similarly, it is apparent that the resultant electrical signals fromelectrodes 28 and the resultant color information can be shown atdisplay unit 26 in different formats to emphasize the relationshipbetween developed signals and the underlying muscle structure. With asuitably high speed computer 25, the images of differing musclestructures can be shown in association with the color patterns asdirected by the physician to provide a correlation between thecolorization and the abnormal muscle elements.

Referring now to FIGS. 24 and 25, there is shown in more detail thecomponents comprising the analog and digital signal portions of theinvention including electrode subsystem 100, analog signal conditioningsubsystem 101, and signal processing subsystem 102. Electrode subsystem100 comprises the array of sixty-three electrodes 28, only a few ofwhich are shown and labeled as A, B, F, G, Ref. and Gnd. incorrespondence with previous descriptions. Wires 40 connect electrodes28 to buffer amplifier 42, shown in block form on FIG. 24 and in moredetail in FIG. 25.

A long shielded interconnect cable 104 connects the outputs of bufferamplifier 42 to more remotely located Filter/Buffer module 105 whichincludes low and high pass filters 43, 44. In turn, a short shield cable45 completes the analog signal portion, being connected to analog todigital converter card 24 in computer 25, the latter components beingessential parts of the signal processing subsystem 102. As indicated, asingle continuous shield path, depicted by dashed lines 107, isestablished between Buffer/Amplifier module 42 and computer 25, assuringthat minimal interference is generated in the signals of interest fromextraneous sources.

The enclosures used for the Filter/Buffer module 105 and theBuffer/Amplifier module 42 are shielded with a layer of conductivematerial. All enclosure shields are connected in series with theinterconnect cable shields, resulting in a single continuous shield pathfrom the Buffer/Amplifier input connector to the data acquisitioncomputer 25 chassis ground.

The array of electrodes 28 mounted on sensor pad 10, as previouslydescribed, must conform to the human back, ensure consistent electrodeimpedance with the skin, not interfere substantially with patientmovement, and be easy to clean and reuse. The electrodes 28 arepreferably in a nine row by seven column configuration and the sensorpad 10 is preferably held in place with a fabric brace with or withoutpressure sensitive adhesive.

The analog signal conditioning subsystem 101 provides buffering, voltageamplification and analog filtering for the array of electrodes 28. Oneelectrode in the array is designated as the reference electrode 61, andall other electrode voltages are measured with respect to the referenceelectrode 61.

Each of the electrode 28 signals is connected by way of wires 40 to highimpedance, unity gain buffer amplifiers 108 by way of a 10K Ohm seriesresistor 109. The purpose of resistor 109 is to provide a measure ofresistive isolation for safety purposes, as well as to increase theelectrostatic discharge (ESD) immunity of the amplifier.

Following the buffer amplifiers 108, each channel has a dedicated highgain instrumentation amplifier 110. The inverting input of eachinstrumentation amplifier 110 is connected to the buffered signal fromthe reference electrode channel as shown by connector 111. Thus, theoutput of each instrumentation amplifier 110 represents the voltage of agiven electrode with respect to the reference electrode 61. RC networks112 connected to the inputs of the instrumentation amplifier 110 serveas low pass filters to block unwanted high frequency signals. Theoutputs of the instrumentation amplifiers 110 feed into unity-gain,line-driver circuits 114 that are capable of driving the capacitive loadof the long shielded interconnect cable 104, without oscillation.

The ground electrode 31 is connected to the patient and is connected toground through a resistor. In the preferred embodiment electrode 31 isconnected to the analog signal ground on the digital converter cardthrough a one million Ohm resistance. The preferred form of the analogto digital converter card 24, is a sixty-four channel multiplexedconverter capable of operating in pseudo-differential input mode. TheBuffer/Amplifier module 42 and Filter/Buffer module 105 are eachconnected to ground as represented by line 106.

Each of the sixty-three signal inputs into Filter/Buffer 105, via cable104, is connected to a second order active low pass filter 43. Theoutput of low pass filter 43 is connected to the input of first order,high pass filter 44. The output of each high pass filter 44 is connectedto unity gain buffer 115 that is capable of driving the capacitive loadof the analog to digital converter card 24 interconnect cable 45,without oscillation. Electronic power for Filter/Buffer module 105 isprovided by an external linear power supply. Filter/Buffer module 105provides power for Buffer/Amplifier module 42 via the interconnect cable104. Ground sense line 106 from the Buffer/Amplifier modules 42 passesdirectly through the Filter/Buffer module 105.

Signal processing subsystem 102 is shown in block diagram form in FIG.26 and consists of the major elements of a digital filter 120, voltagedifferencer 121 and RMS calculator 122. First, digital filteringtechniques are used to reduce noise on the measured signal. Next, avoltage differencer 121 determines the voltage waveform between alladjacent electrodes 28. Finally, the root-mean-square (RMS) voltagebetween all adjacent electrodes is calculated and used to characterizethe level of muscle activity between adjacent electrodes. The signalprocessing subsystem is preferably implemented in software on aPC-compatible computer 25.

The digital signal conditioning system consists of high pass, low passand band-cut digital filters incorporated into the data analysissoftware. The high and low pass filters are designed to reject signalsoutside of the frequency range of interest, and have amplitude rolloffsof 80 dB/decade. The primary purpose of these digital filters is toblock common-mode error signals introduced near the corner frequenciesof the analog filters. The band-cut or notch filter drastically reduces60 Hz signals, in order to eliminate unwanted pickup of power lineemissions. In one preferred form of the invention oversampling is usedwhich interpolates additional pseudo sample points between actual samplepoints to improve performance of filters, for example to achieve goodfrequency discrimination in the 60 Hz notch filter. In one preferredembodiment 10× oversampling is used.

The output of the electrode voltage data acquisition subsystem consistsof a set of voltage waveforms of each electrode 28 with respect to aparticular reference electrode. The voltage differencer 121 computes thevoltage waveform between each pair of adjacent electrodes (vertically,horizontally and diagonally) by differencing the voltage waveforms forthe two adjacent electrodes. RMS calculator 122 provides the RMS valueof each adjacent electrode pair waveform as a scalar number which iscomputed from the waveform using a conventional RMS calculation.

The user display subsystem 26 presents the processed data to thepractitioner in a readily understandable format. The data is displayedas images on a screen or other visual output device. A digitizedillustration of a muscle layer in the human back as shown in FIGS. 14-23is used as the background of the image. The user may select any musclelayer as the image background. A computer generated image 125 of theprocessed electrode 28 data is overlaid on the selected backgroundillustration, and is spatially registered to that image.

The electrode data image 125 consists of colored lines or light bars 63drawn between the locations of each of adjacent electrodes 28, which areat each intersection 128 of each of the seven vertical columns and ninehorizontal rows of light bars 63 as shown in FIG. 3 and as has beenpreviously described. The color of each line 63 indicates the value ofthe RMS voltage between the adjacent electrodes. The user candynamically specify a maximum RMS value and a minimum RMS value whichare used to map voltages to colors. The resulting display is thus afalse-color RMS voltage gradient field display, and is overlaid on andregistered to the underlying muscle layer illustration.

The software architecture of the signal processing system 102 is shownschematically in FIG. 27 as a diagram of the main data flow in thesoftware. Essentially, this is a linear flow of computations, each ofwhich takes a datum or file as input and generates a datum or file asoutput. Three types of data files are generated and stored and oncecreated may be opened and displayed many times at later dates. The datafiles are described as well in FIG. 29 and comprise the Analog toDigital (A2D) file 130, Voltage (DAT) file 132 and Root Mean Square(RMS) file 134.

The format of header 135 for each of the files, 130, 132, 134 isdepicted in FIG. 28 and in one embodiment contains information in anidentical ASCII header format consisting of version information 152,patient information 154, which are the vital statistics on the patientbeing diagnosed, pad information 155 which provides specifics of sensorpad 10, calibration information 156, data acquisition settings 157 anddisplay settings 158. The calibration information is derived after thesensor pad 10 location is determined on the back of the patient, beinginput by the operator to specify where certain parts of the patient'sback are in relation to the electrodes on the pad, as previouslydescribed.

The A2D files 130 contain the actual analog to digital values at theoutput of analog to digital converter 24 which are collected during atest. Computer 25 scans all electrode channels rapidly enough toreconstruct the analog signal at all frequencies of interest. In oneembodiment the minimum frequency of interest is about 30 Hz and themaximum about 150 Hz. The structure of the A2D files 130 is shown inFIG. 29 with each scan sample being stored in a two byte word in littleendian format. The files 130 contain the analog to digital value and aheader 135.

The voltage files 132 contain the voltage data from a test, after it hasbeen converted from analog to digital values to voltages and signalconditioning filters have been applied. The voltage files 132 of thisembodiment also contain the header 135 followed by the voltage values inthe format shown in FIG. 29, each sample being stored as an IEEE doublefloating point value.

The RMS files 134 contain the RMS values of the differences between thevoltage waveforms of adjacent electrodes 28. During display of an RMSfile 134, the values can be mapped to colors and displayed as coloredline segments or color bars 63 at display unit 26. Again, the RMS files134 contain header 135 followed by the RMS information. The RMS voltagedifference is calculated for each pair of adjacent electrodes 28. Therow and column position of each of the two electrodes are also stored inthe format described in FIG. 29. Also included is information of theminimum and maximum RMS value in each scan and the total number ofadjacent electrode pairs.

Summarizing then, the flow of data as depicted in FIG. 27 occurs ascomputer 25 generates signals to capture samples 140 from dataacquisition board 24 at the input to computer 25 to create raw data orA2D files 130. Computer 25 then acts to convert the signals to voltageat 142 and run signal conditioning filters 144 to create voltage files132. Computer 25 is then programmed to compute the RMS values at 146 andcreate the RMS data file 134. Subsequently, computer 25 operates toscale and compute color values at 148, and then to draw the RMS data at150 and eventually provide the color bar matrix 125 depicted in FIG. 3.

The general architecture for the software operated in computer 25 can beseen from the source file 160 structure depicted in FIG. 30. Thedocument view and visual interface 161 contain main initialization, menuand toolbar commands, message handlers and document/view commands.Dialog popups 162 allow for entering patient information, calibrationinformation and the like and for editing various parameters. Furtherfiles include data acquisition, filtering and calculation 163, readingand writing header information and data 164, utilities 165, and bitmaps,icons and resource files 166. These routines are fairly typical forhandling the information flow in the ways specified previously and arewell understood in the art, not requiring detailed description herein.

Although certain embodiments of the present invention have beendisclosed and specifically described herein, these embodiments are forpurposes of illustration and are not meant to limit the presentinvention. Upon review of this specification, certain improvements,modifications, adaptations and variations upon the methods and apparatusdisclosed which do not depart from the spirit of the present inventionwill immediately become apparent. Accordingly, reference should be hadto the appended claims in order to ascertain the true scope of thepresent invention.

For example, the apparatus of the invention might be applied to areas ofhuman anatomy other than the lower back musculature, most obviously tomid-back, upper back or neck areas. Still further, it would be feasibleto apply the teachings of the invention to the extremities of the humanpatient or even to areas of the head. The present invention may also beapplied to the analysis of signals from other types of sensors and thetechniques described herein used in the diagnosis and treatment of otherconditions. While the preferred form of the invention is used in thediagnosis of conditions in human beings, the techniques and apparatus ofthe invention may also find applicability in diagnostic and treatmentactivities related to patients which comprise other living organisms.

Thus the method and apparatus of the present invention achieve the abovestated objectives, eliminates difficulties encountered in the use ofprior devices and systems, solves problems and attains the desirableresults described herein.

In the foregoing description certain terms have been used for brevity,clarity and understanding. However no unnecessary limitations are to beimplied therefrom because such terms are for descriptive purposes andare intended to be broadly construed. Moreover the descriptions andillustrations herein are by way of examples and the invention is notlimited to the details shown and described.

In the following claims any feature that is described as a means forperforming a function shall be construed as encompassing any meanscapable of performing the recited function and shall not be limited tothe particular means shown in the foregoing description or mereequivalents.

Having described the features, discoveries and principles of theinvention, the manner in which it is constructed and operated and theadvantages and useful results attained; the new and useful structures,devices, elements, arrangements, parts, combinations, systems,equipment, operations and relationships are set forth in the appendedclaims.

What is claimed is:
 1. An electrode for collecting surfaceelectromyographic (EMG) signals from a skin surface of a patient,comprising:an electrically conductive head member having apatient-contact surface thereon; a plurality of pyramids disposed on oneside of said head member forming the patient-contact surface, whereineach pyramid includes a pointed tip at an apex of the pyramid; said headmember being of a shape to conform to the skin surface of a patient; andsaid pointed tips being of substantially uniform elevation from saidhead member in order to uniformly contact the skin surface of thepatient.
 2. The electrode as set forth in claim 1 wherein said pointedtips are arranged in a uniform array at one side of said head member andare substantially equally spaced from one another.
 3. The electrode asset forth in claim 2 wherein each of the pyramids includes asubstantially square base, wherein the pyramids are integral with theconductive head, and wherein the pyramids project outwardly from thehead member.
 4. The electrode as set forth in claim 3 wherein saidpyramids are formed by grinding or electromachining said conductivehead.
 5. The electrode as set forth in claim 3 wherein said head memberis a circular disc and is substantially planar.
 6. The electrode as setforth in claim 5, further comprising a shaft integral with said headmember for supporting said head member in patient-contacting position,said shaft being orthogonal to the plane of said head member.
 7. Theelectrode as set forth in claim 6 wherein said shaft is electricallyconductive to transmit signals from said head member, and is threaded toreceive a nut for securing said electrode in an aperture of a supportmember.
 8. An electrically conductive electrode for gathering electricalsignals from the body surface of a patient, comprising:an electricallyconductive, generally bolt-shaped structure having a head and integralshaft orthogonal to the head; a plurality of pointed members integralwith and projecting outwardly of the head, wherein each of the pointedmembers terminates in a tip, wherein all of the tips lie substantiallyin a plane and equidistantly spaced outwardly of the head, and whereinthe tips have a substantially uniform elevation from the head in orderto uniformly contact the skin surface of the patient; the shaft beingthreaded to receive a nut for securing the electrode in an aperture of asupport member.
 9. The electrode as set forth in claim 8 wherein saidhead is in the shape of a disc and said tips are disposed in asubstantially equally spaced array outwardly of said head.
 10. Anelectrically conductive electrode for gathering electrical signals fromthe body surface of a patient, comprising:an electrically conductive,generally bolt-shaped structure having a head and integral shaftorthogonal to said head; a plurality of pyramids integral with andprojecting outwardly of the head, wherein each of the pyramidsterminates in a tip, wherein the pyramids have flat sides, joined at theapex of each pyramid to form the tips, wherein all of the tips liesubstantially in a plane and equidistantly spaced outwardly of the head,and wherein the tips have a substantially uniform elevation from thehead in order to uniformly contact the skin surface of the patient; theshaft adapted to receive a securing member for mounting the electrodeand for transmitting electrical signals between the head and a remoteutilization device.
 11. The electrode as set forth in claim 10 whereineach said pyramid comprises a substantially square base and saidpyramids are formed by machining of said head.
 12. The electrode as setforth in claim 11 wherein said pyramids are formed by grinding of saidhead in a series of parallel and orthogonal passes.
 13. The electrode asset forth in claim 11 wherein said pyramids are formed byelectromachining.
 14. An electrically conductive electrode for gatheringelectrical signals from the body surface of a patient, comprising:anelectrically conductive, generally bolt-shaped structure having a headportion and integral shaft portion extending generally orthogonal tosaid head, wherein said head is in the shape of a disc, wherein saidhead diameter is approximately 0.375 inch; a plurality of pyramidsintegral with and projecting outwardly of the head portion, wherein eachof the pyramids has a substantially square base and flat sides thatintersect at an apex of each pyramid to form a tip, wherein all of thepyramid tips lie substantially in a plane and are disposed in asubstantially equally spaced array, and wherein the pyramids are formedby machining the head portion, and wherein the head thickness includingthe pyramids is approximately 0.08 inch, wherein the pyramid altitude isapproximately 0.042 inch, and wherein the tip radius is approximately0.005 inch; and wherein the shaft portion is adapted to receive asecuring member enabling mounting the electrode and wherein the shaftportion transmits electrical signals from the head portion, wherebysignals from the head portion may be received by a remote signalutilization device.
 15. The electrode as set forth in claim 14 whereinsaid electrode is formed entirely of 316L stainless steel and said tipspacing is on the order of 0.094 inch.
 16. The electrode as set forth inclaim 15 wherein the number of said pyramids is on the order of
 12. 17.An electrode for collecting surface electromyographic (EMG) signals froma skin surface of a patient, comprising:an electrically conductive headmember having a patient-contact surface thereon, wherein the head memberincludes a integral shaft orthogonal to said head; a plurality ofprojections disposed on one side of the head member forming thepatient-contact surface, wherein each of the projections has a broadbase tapering to a pointed apex; the head member being of a shape toconform to the skin surface of a patient; the projections being ofsubstantially uniform elevation from the head member in order touniformly contact the skin surface of the patient; and the shaft beingthreaded to receive a nut for securing said electrode in an aperture ofa support member.
 18. An electrode for collecting surfaceelectromyographic (EMG) signals from a skin surface of a patient,comprising:an electrically conductive head member having apatient-contact surface thereon; a plurality of projections disposed onone side of the head member forming the patient-contact surface, whereineach of the projections has a broad base tapering to a pointed apex,wherein each projection has an apex radius of approximately 0.005 inch;the head member being of a shape to conform to the skin surface of apatient; and the projections being of substantially uniform elevationfrom the head member in order to uniformly contact the skin surface ofthe patient.